The 10-bit display mode is off when the option "Force Composition Pipeline" enabled

Hi guys:

We use P1000 with linux driver 390.48. We want to display in 10-bit mode. It works fine when "Force Composition Pipeline" is disabled. But if the "Force Composition Pipeline" is enabled(For fixing the screen tearing issue), 10-bit is gone. Any ideas? Thanks.

But with the linux driver 384.111 or older version, it's no above issue(Whether or not the "Force Composition Pipeline" was enabled), the 10-bit mode always take effect.

OS: CentOS 6.6
Xorg version: 1.15.0